Cumene is a product of commercial interest that is used as raw material in the production of phenol and acetone. Numerous processes have been developed using acid catalysts. A general reference on the catalysts and processes used can be found in “Encyclopedia of Chemical Processing and Design”, J. J. McKezta and W. A. Cunningham Editors, V. 14, pp. 33-55 (1982). The alkylation of benzene with propylene, in addition to seeking a high conversion of propylene and a high selectivity for the monoalkylated product, isopropylbenzene (cumene), requires a minimum amount of n-propylbenzene (NPB) be formed. This is because NPB interferes with the oxidation of cumene to produce phenol and acetone, and consequently there is a need for a stream of cumene with the least amount of NPB impurities possible. Since it is difficult to separate cumene from NPB by conventional methods, such as distillation for example, then, logically, the yield of NPB must be as low as, possible, and at any rate very low, during the alkylation or benzene with propylene.
From the viewpoint of the catalysts used in this process, acids such as H3PO4, AlCl3 and HCl have conventionally been used, although they do give‘ rise to problems arising from corrosion and loss of selectivity owing to the formation of polyalkylated products. Zeolites have also been used as catalysts for the alkylation of aromatics; thus, for example, patent U.S. Pat. No. 4,292,457 describes zeolite ZSM-5 as a catalyst for the alkylation of benzene with propylene.
However, probably owing to the small diameter of its channels, this zeolite proves to be not very selective for the desired process. There are also many patents that describe the use of Faujasite and modified Faujasites as catalysts for the production of cumene by alkylation of benzene with propylene. More specifically, zeolite Y has good activity at temperatures of between 130 and 180° C., with good selectivity for the desired products. However, this selectivity decreases sharply when the conversion of benzene is increased, and it is therefore necessary to work with high benzene/propylene ratios in the feed. This results in high benzene recycling costs. Zeolite Beta has also been claimed as a catalyst for the alkylation of benzene with propylene in various patents, such as U.S. Pat. No. 4,891,458, U.S. Pat. No. 5,030,786, EP 432 814, EP 439 632, and EP 629 599. This zeolite produces good results in terms of activity and selectivity, but its performance can be improved as regards both selectivity for NPR and the stability of the catalyst.
Spanish patent application P200101145 describes a zeolite material called ITQ-21. However, it does not disclose a process for the alkylation of aromatic products with olefins and alcohols or polyalkylated aromatics in which this zeolite is used as catalyst. Spanish application P20012287, also, relates to said crystalline solid material, specifically to its use in cracking, but it does not describe an alkylation process according to the present invention.
The subject of the present invention is a process for the alkylation of aromatic products with olefins and alcohols or polyalkylated aromatics in the presence of a catalyst with an X-ray pattern and a chemical composition corresponding to ITQ-21, this catalyst being not only active but also, in the case of cumene, producing a very low yield of n-propylbenzene, an unwanted product.